The cerebral cortex of the rat contains an anatomically distinct area consisting of cylinders of neurons or "barrels" in lamina IV of somatic sensory area I (SI). All neurons of an individual barrel are excited by movement of a single contralateral mystacial vibrissa. As a follow-up to our light microscopic study of the barrel projections from the thalamic ventrobasal complex (VB), we shall determine, using the electronmicroscope the fine structure of the normal barrels and the mode of termination of thalamocortical afferents following either large lesions or tritiated amino acid injections of VB. In addition, the relationship of a single or combinations of vibrissa(e) with the cortical barrel(s) of lamina IV and the other laminae of the barrel region of SI will be investigated using the (14C)-2 deoxy-d-glucose (2 DG) metabolic mapping technique. Utilizing the 2 DG method, alterations of the developing barrels will be examined following ablation of different combinations of vibrissal follicles in newborn rats.